The special forces – the SAS and its naval equivalent, the Special Boat Service (SBS) – have always been treated as a special case, protected by a ring of official secrecy.

The court martial paid lip service to the convention that their members and their operations are not mentioned by name. Thus, Nightingale was said to be a member of a "unit" that was surrounded by a certain mystique, as the prosecuting counsel put it. Their bases in Iraq were referred to as North 1, North 2, and South.

That mystique has fed a special status that has encouraged SAS troopers to believe they are not bound by the same rules as other soldiers in the British army; keeping trophies after foreign deployments was often regarded as "half-OK", as one of Nightingale's former colleagues put it.

The jailing last year of Nightingale provoked a storm of protest. More than 35,000 people signed a petition calling for the case to be reviewed. Tory MPs joined those who expressed outrage at his jailing.

Julian Brazier, the Tory MP for Canterbury and a former member of the territorial SAS, said Nightingale had "risked his life for his country again and again".

Philip Hammond, the defence secretary, joined in asking the attorney general, Dominic Grieve, "to review whether the public interest test has been applied appropriately".

David Cameron's official spokesman said: "The PM agrees that the defence secretary was right to pursue every avenue and make sure that the correct processes had been followed."

Grieve and other government lawyers were not amused. A spokesperson for Grieve said it would be inappropriate for him to review "either the decision to prosecute or comment on the appropriateness of the sentence. That is a matter for the court martial appeal court, in due course."

Army commanders were as uneasy as government lawyers. They did not like the way the SAS got away with special treatment, epitomised by an amnesty for those keeping weapons unlawfully, introduced after Nightingale was arrested.

The feeling that the SAS is unfairly protected is compounded by the fact that the official rule – still adhered to by the D notice committee, which runs a system of voluntary self-censorship with the media – that their operations should never be identified is honoured far more in the breach than in the observance.

The media are not discouraged from referring to SAS exploits when they are successful. When they have been involved in controversial activities, such as helping to send terror suspects to prisons where they were abused, questions from journalists are met with silence.

The issues are particularly serious at a time when Britain's special forces have been deployed more than ever since the second world war. And they are likely to play an increasingly significant role in future conflicts.